LM317 Application Notes Example

I was messing around a while ago to modify my Norcal QRP Club Power Meter kit so that I could power it from the shack DC supply. The kit takes a 9V battery by default and I wanted to power it from the 13.8V shack supply. I didn’t have an LM7809 handy but I did have an LM317. I also didn’t want to mess around with a variable trim on the supply so I looked at the oddball combination of resistors that I had on hand and decided to draw the curves for the LM317 against all the combinations I could make fairly easily (parallel and series for any two).